Conventional air-conditioning apparatuses mainly use R410A, which is an HFC refrigerant, as a refrigerant filled into a refrigerant circuit. R410A has an ozone depletion potential (ODP) of zero and does not deplete the ozone layer, unlike conventional HCFC refrigerants such as R22, but has the property of high global warming potential (GWP). Consequently, to prevent global warming, the trend is setting toward an HFC refrigerant with a low GWP from an HFC refrigerant such as R410A with a high GWP.
Examples of such low-GWP HFC refrigerants include halogenated hydrocarbons having carbon double bonds in the composition, and the representative examples include HFO-1234yf (CF3CF═CH2, tetrafluoropropane), HFO-1234ze (CF3-CH═CHF), and HFO-1123 (CF2=CHF). These refrigerants are types of HFC refrigerants, but are often referred to as HFO using the initial (O) of olefin because unsaturated hydrocarbons with carbon double bonds are often called olefins. Thus, the unsaturated hydrocarbons with carbon double bonds will be referred to herein as HFO refrigerants in distinction from HFC refrigerants without a carbon double bond in the composition, such as R32 (CH2F2, difluoromethane) and R125 (CHF2-CF3, pentafluoroethane) included in R410A.
Such a low-GWP HFO refrigerant can be used as a single component refrigerant, but is highly likely to be used as a mixture of plural refrigerants in combination with an HFC refrigerant as typified by R32. The HFO refrigerant or a mixture of HFO refrigerant and HFC refrigerant is not highly flammable as HC refrigerant such as R290 (C3H8, propane), but is mildly flammable unlike R410A, which is non-flammable. Consequently, care must be taken against refrigerant leakage, and hereinafter a refrigerant having any of flammability levels ranging from mild flammability to high flammability will be referred to as a flammable refrigerant. R32 as a single component refrigerant has mild flammability similarly to the HFO refrigerant, that is, a mixture of HFO refrigerant and R32, which are flammable, is also flammable. Note that R410A, which is a mixture of R32 and R125, is non-flammable due to a property of R125.
Generally, refrigerant can leak due to a poor connection or corrosion of a refrigerant pipe configured to circulate refrigerant between an indoor unit and an outdoor unit. Unless measures are taken, the leaking refrigerant can accumulate in the indoor unit at a concentration no lower than a flammable concentration. If the leaking refrigerant reaches a high concentration and flows out of the indoor unit and an ignition source is close to the indoor unit, the leaking refrigerant may catch fire. The ignition may damage, for example, a surface of the indoor unit. Thus, to prevent ignition of the leaking refrigerant, measures need to be taken.
Patent Literature 1 discloses a configuration in which refrigerant leaking out of a heat exchanger placed in a heat exchange chamber is caused to flow into a pipe chamber through a drain pan and the refrigerant leakage is detected by a sensor provided in the pipe chamber. Any leaking refrigerant detected is blown out of the indoor unit by operating a fan. This configuration prevents refrigerant from accumulating in the indoor unit at a concentration no lower than a flammable concentration. According to Patent Literatures 2 and 3, a hole is formed in a house wall, a pipe of an air passageway extending from the outdoor unit is passed through the wall, and leaking refrigerant is caused to flow outdoors through the air passageway.